UPDATE 4-Brexit is in peril, UK PM May warns ahead of vote on her deal

Prime Minister Theresa May warned
on Monday that Britain's planned exit from the EU could be
derailed, a last-ditch effort to win over Brexit-supporting
lawmakers who have repeatedly said they will vote down her
divorce deal.

The fate of the United Kingdom's March 29 exit from the EU
is deeply uncertain as parliament is likely to reject May's deal
on Tuesday evening, opening up outcomes ranging from a
disorderly divorce to reversing Brexit altogether.

Amid the deepest crisis in British politics for at least
half a century, May and EU leaders exchanged letters giving
assurances on her withdrawal agreement, though there was little
sign of a change of heart among rebel lawmakers.

May used a speech at a china factory in the leave-supporting
city of Stoke-on-Trent in central England to say that lawmakers
blocking Brexit altogether was now a more likely outcome than
Britain leaving without a deal.

"There are some in Westminster who would wish to delay or
even stop Brexit and who will use every device available to them
to do so," May said.

"While no-deal remains a serious risk, having observed the
events at Westminster over the last seven days, it's now my
judgment that the more likely outcome is a paralysis in
parliament that risks there being no Brexit."

As the world's biggest trading bloc tried to brace for an
unpredictable ride, Spain said the EU could agree to extend the
deadline for Brexit, but not beyond elections for the European
Parliament due in May.

May warned lawmakers on Sunday that failing to deliver
Brexit would be "catastrophic" for democracy, and her ministers
said that thwarting the outcome of the 2016 referendum could
lead to rise in far-right populism.

LETTER FROM EU

As part of the effort to get the deal approved by the
British parliament, the EU and May set out some assurances in a
choreographed exchange of letters on Monday.

The EU told May that it stood by commitments to find ways to
avoid triggering the controversial "Irish backstop" in their
Brexit deal and that this pledge had legal weight.

In a joint reply to questions from May, European Commission
President Jean-Claude Juncker and European Council President
Donald Tusk said the EU stood by its commitment to try and reach
a post-Brexit trade deal by the end of next year in order to
avoid using the unpopular backstop.

While stressing that nothing in their letter could be seen
as changing or being inconsistent with the draft treaty agreed
with May last month, they said a commitment to speedy trade deal
made by EU leaders had "legal value" which committed the Union
"in the most solemn manner".

However, even if the target date were not met, they wrote,
Britain would have the option to extend a status-quo transition
period to avoid triggering the backstop, which is meant to avoid
a hard customs border for Northern Ireland.

"If the backstop were nevertheless to be triggered, it would
only apply temporarily, unless and until it is superseded by a
subsequent agreement that ensures that a hard border is
avoided," they said.

May said the assurances might not go far enough for some
lawmakers and the small Northern Irish party that props up her
government said it was insufficient.

But with her deal facing opposition from all sides in the
lower house of parliament, the House of Commons, the letters are
unlikely to change the fundamental outcome of the vote.

"PARLIAMENT PLOT"

With no-deal Brexit the default option if May's deal is
defeated, some lawmakers are planning to pull control of Brexit
from the government.

Though May is weakened, the executive has significant
powers, especially during times of crisis, so it was unclear how
parliament would be able to take control of Brexit.

If May's deal is defeated and the government is unable to
have any amended version passed in the next three weeks, one
suggestion is for senior lawmakers who chair parliamentary
committees to come up with an alternative Brexit plan.

"We're in the very, very final stages of the end-game here,"
said Nick Boles, one of the Conservative lawmakers behind the
plan, who said he would vote for May's deal.

"What we need to do is find the solution, and if the
government can't find the solution -- and we want the government
to find the solution, and we'll be voting for her solution --
but if it can't then parliament needs to," he told BBC radio.
(Additional reporting by Jan Strupczewski in Brussels
Writing by Guy Faulconbridge
Editing by Michael Holden and Catherine Evans)